FIELD OF THE INVENTION
The invention relates to a rotor for a turbine, particularly a steam turbine, including individual rotor parts being welded together to make a unit, and to a method for producing the turbine rotor.
The rotor of a turbine used to generate electrical power, such as a steam turbine, is subjected to severe strains. In order to withstand them and to nevertheless achieve long service times on one hand while keeping production costs within acceptable limits on the other hand, many possible constructions have been conceived of, all of which have certain advantages but naturally also have disadvantages.
An especially sound but also complicated and expensive production method is to forge a one-piece rotor from a solid block. The procurement of material required for production cannot be done until an order has been received and often involves a long delivery time, which is not in the least due to the fact that the number of available shippers is limited. Moreover, prefabrication independently of orders and parallel machining of individual parts are not possible, resulting in long production times. The use of rotor disk blades also presents difficulties, when it involves axially insertable blade roots, since machining the grooves requires a greater axial spacing between the rotor disks, to enable working with suitable tools. However, wide spacings between the rotor disks worsen the rotor dynamics.
Another construction makes it possible to produce suitable rotors with separate, shrink-fitted-on rotor disks. However, in the shrinking process, additional strains arise in the rotor, and moreover there is the danger of corrosion from friction at the joints. It is also known to screw together disks that mesh with one another through a tie rod, but that is not unproblematical either, since over the long term loosening of the screwed connection must be expected.
Some of those disadvantages can be averted by forming individual rotor segments and then welding them together to a unit that forms the rotor. Such rotors are known, for instance, from the BBC Corporate Publication entitled "Geschwei.beta.te Rotoren fur Dampfturbinen" [Welded Rotors for Steam Turbines], Publication No. CH-T 060 072 D, and from German Published, Non-Prosecuted Applications DE 22 35 961 Al and DE 25 22 277 Al. However, the disadvantages of rotors of that type are that conventional welding techniques are employed and that since the individual segments are merely premachined parts, extensive post-machining is required.
That means that the rotor must be machined in final form in the form of a large, heavy single piece, as in the case of a rotor forged from the solid block. The segmentation and further provisions are intended to make the rotor lighter.